Biomechanics on the mechanical adaptation of biological tissues at the microstructural level

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We developed a new method by which tensile tests were performed observing the microstructure of the chemically non-treated raw collagen fascicles with a phase-contrast microscope or differential interference microscope, and studied the relationships between the microstructure and mechanical properties of fascicles obtained from the mouse tail tendon.For mechanical testing, a specially designed micro tensile tester was mounted on a microscope. Small acrylic blocks were attached to both ends of each fascicle with cyanoacrylate adhesives. One of the blocks was fixed to a load cell, and the other one was fixed to the crosshead of a linear actuator. The fascicle was immersed in a saline solution and sandwiched between a slide glass and cover glass. The specimen was stretched to failure by moving the actuator at the speed of 0.1 mm/sec. The microstructure of the fascicle was observed using the microscope, and the images were recorded on a digital video recorder.Microscopically, the bundles of collagen fibers arranged in a typical parallel fashion were observed in the fascicles. Under no load, the bundles had a periodic crimp pattern. At the liner region of load-deformation curve, the fibers were straightened in parallel. Before the catastrophic decrease of load, the partial rupture of some fibers was observed.